// Copyright 2013 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
//
// Manages the packet entropy calculation for both sent and received packets
// for a connection.

#ifndef NET_QUIC_QUIC_SENT_ENTROPY_MANAGER_H_
#define NET_QUIC_QUIC_SENT_ENTROPY_MANAGER_H_

#include <deque>

#include "base/macros.h"
#include "net/base/linked_hash_map.h"
#include "net/quic/quic_framer.h"
#include "net/quic/quic_protocol.h"

namespace net {

namespace test {
    class QuicConnectionPeer;
} // namespace test

// Records all sent packets by a connection to track the cumulative entropy of
// sent packets.  It is used by the connection to validate an ack
// frame sent by the peer as a preventive measure against the optimistic ack
// attack.
class NET_EXPORT_PRIVATE QuicSentEntropyManager {
public:
    QuicSentEntropyManager();
    virtual ~QuicSentEntropyManager();

    // Record |entropy_hash| for sent packet corresponding to |packet_number|.
    void RecordPacketEntropyHash(QuicPacketNumber packet_number,
        QuicPacketEntropyHash entropy_hash);

    // Retrieves the cumulative entropy up to |packet_number|.
    // Must always be called with a monotonically increasing |packet_number|.
    QuicPacketEntropyHash GetCumulativeEntropy(QuicPacketNumber packet_number);

    // Returns true if |entropy_hash| matches the expected sent entropy hash
    // up to |largest_observed| removing packet numbers from |missing_packets|.
    // Must always be called with a monotonically increasing |largest_observed|.
    bool IsValidEntropy(QuicPacketNumber largest_observed,
        const PacketNumberQueue& missing_packets,
        QuicPacketEntropyHash entropy_hash);

    // Removes unnecessary entries before |packet_number|.
    void ClearEntropyBefore(QuicPacketNumber packet_number);

private:
    friend class test::QuicConnectionPeer;

    typedef std::deque<QuicPacketEntropyHash> SentEntropyMap;

    struct CumulativeEntropy {
        CumulativeEntropy()
            : packet_number(0)
            , entropy(0)
        {
        }

        QuicPacketNumber packet_number;
        QuicPacketEntropyHash entropy;
    };

    // Convenience methods to get the largest and smallest packets with entropies.
    QuicPacketNumber GetLargestPacketWithEntropy() const;
    QuicPacketNumber GetSmallestPacketWithEntropy() const;
    // Convenience method to get the entropy hash for |packet_number|.
    QuicPacketEntropyHash GetPacketEntropy(QuicPacketNumber packet_number) const;

    // Update the cumulative entropy to |packet_number|.
    void UpdateCumulativeEntropy(QuicPacketNumber packet_number,
        CumulativeEntropy* cumulative) const;

    // Maps packet numbers to the sent entropy hash for the packet number.
    SentEntropyMap packets_entropy_;
    QuicPacketNumber map_offset_;

    // Cache the cumulative entropy for IsValidEntropy.
    CumulativeEntropy last_valid_entropy_;

    // Cache the cumulative entropy for the packet number used by EntropyHash.
    CumulativeEntropy last_cumulative_entropy_;

    DISALLOW_COPY_AND_ASSIGN(QuicSentEntropyManager);
};

} // namespace net

#endif // NET_QUIC_QUIC_SENT_ENTROPY_MANAGER_H_
